Tutorial title - Main components of the axis - Regulation by TSH

7 important questions on Tutorial title - Main components of the axis - Regulation by TSH

How is TRH secreted?

There is pulsatile secretion, with evidence of circadian and seasonal secretion. It is also more readily released in younger organisms.

Can too much iodide lead to hyperthyroidism?

No, the wolff-chaikoff effect stops iodine trapping and organification when there is an excess of iodide

What is the ratio of T4 and T3 secretion?

4:1
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Where is the majority (60-75%) of T3 produced?

In the liver and kidneys by deiodinases (peripheral conversion of T4)

What is the ratio of T4 and T3 in the plasma?

20:1

What are the half lifes of each thyroid hormone?

T3: 1 day, 3-5x more potent than T4
T4: 6-7 days, PREHORMONE

Are all thyroid hormones biologically active?

No, only free T3 and T4 are biologically active. >99% of TH bound by TBH

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